This invention relates generally to dynamoelectric machines and, more particularly, to motor control circuits for an electronically commutated brushless direct current motor.
Dynamoelectric machines are utilized in many manufacturing applications. Dynamoelectric machine failures can cause lost production time, injury to personnel, and loss of capital equipment, all of which can reduce profitability. Therefore, a dynamoelectric machine manufacturer typically tests a motor before the motor leaves a production facility. An electronically commutated motor (ECM) typically includes a motor housing, a stator mounted to the housing, and a rotor shaft rotatably mounted within a bore of the stator. A rotor core is mounted on the rotor shaft and includes a plurality of permanent magnets. The stator includes a stator core including a plurality of electrically excitable windings. The stator windings generate a plurality of magnetic fields that oppose magnetic fields from the permanent magnets on the rotor. For the rotor to turn, the windings on the stator reverse polarity through commutation. A brushless commutator placed on one end of the rotor provides a signal to the stator windings to reverse polarity. In certain known ECMs, an integrated circuit times the switching of the electric currents to the stator. Frequently, a programmable chip is used with the brushless DC motor to provide multispeed capabilities. Typically, the programmable chip utilizes pulse width modulation (PWM) to control the speed of the motor.
Typically, the PWM input is applied through a two-wire interface in a control housing. The two-wire interface is unidirectional and does not provide feedback useful for testing purposes. Therefore, conventional motors also include a three wire bi-directional interface that a motor manufacturer uses for factory testing the motor. The three-wire interface is also in the control housing and from a customer perspective adds unnecessary lead wires to the control housing.
In one embodiment, a method for utilizing a three-wire programming box with a motor control circuit is provided. The method includes providing a three-wire to two-wire interface. The method further includes connecting the three-wire to two-wire interface between the three-wire programming box and the motor control circuit such that the three-wire programming box communicates bi-directionally with the motor control circuit utilizing less than three connections between the three-wire to two-wire interface and the motor control circuit.
In another embodiment, an interface circuit for interfacing with a motor control circuit including a first input circuit is provided. The interface circuit includes a three-wire to two-wire interface including a second input circuit electrically equivalent to the first input circuit of the motor control circuit.
In a further embodiment, a motor control and testing circuit includes a first input circuit, a second input circuit coupled to the first input circuit, and a microcontroller connected to the second input circuit. The circuit further includes a first output circuit coupled to the microcontroller, and a second output circuit coupled to the first output circuit. The second output circuit is connected to the first input circuit and is configured to send outputs from the microcontroller to the first input circuit.
In another embodiment, a motor control and testing circuit includes a first input circuit, a second input circuit coupled to the first input circuit, and a microcontroller connected to the second input circuit. The circuit further includes a first output circuit coupled to the microcontroller, and a second output circuit coupled to the first output circuit. The second output circuit is connected to the first input circuit and is configured to send outputs from the microcontroller to the first input circuit. The circuit further includes a third input circuit electrically equivalent to the first input circuit, and a comparator. The third input circuit and the first input circuit are connected to the comparator forming an impedance bridge.
In a further embodiment, an electrically commutated motor includes a housing, and a stator including a plurality of windings and a bore therethrough. The stator is mounted in the housing. The motor further includes a rotor shaft extending at least partially through the bore, and a rotor core mounted on the rotor shaft. The rotor core includes a plurality of magnets. The motor also includes a commutator connected to the windings, and a motor control and testing circuit connected to the commutator. The motor control and testing circuit includes a first input circuit, a second input circuit coupled to the first input circuit, and a microcontroller connected to the second input circuit. The motor control and testing circuit further includes a first output circuit coupled to the microcontroller, and a second output circuit coupled to the first output circuit. The second output circuit is connected to the first input circuit and is configured to send outputs from the microcontroller to the first input circuit.